Common Failures in Boiler Tubes and How to Prevent Them
Quick answer – the most common boiler tube failures
Most boiler tube failures come from five causes: overheating (long-term creep or short-term loss of cooling), water-side corrosion (caustic gouging, hydrogen damage, oxygen pitting), erosion (fly ash and sootblowers), fatigue (corrosion fatigue and thermal fatigue) and fireside corrosion. They are prevented by good water chemistry, keeping metal temperatures within design, controlling erosion, gentle start-ups and regular NDT inspection – and by using the right tube grade for each section of the boiler.
Boiler tubes run at high pressure and temperature, with water or steam inside and hot, ash-laden gas outside. When one fails, the unit usually has to come off line, so knowing why boiler tubes fail – and spotting the early signs – saves both outages and money. Below are the main failure mechanisms, how to recognise each one, and how to prevent it.
Boiler Tube Failure Mechanisms at a Glance
| Failure mechanism | Where it occurs | What it looks like | Root cause | Prevention |
| Long-term overheating (creep) | Superheater, reheater | Thick-lipped rupture, swelling, internal oxide scale | Metal runs above design temperature for months – steam-side scale, wrong grade, flue-gas imbalance | Correct alloy (e.g. T22, T91), monitor metal temperatures, remove oxide scale, replace tubes at end of creep life |
| Short-term overheating | Water walls, superheaters | Thin-lipped, “fish-mouth” rupture | Sudden loss of flow or cooling – blockage, low drum level, start-up without flow | Clear blockages, control drum level and start-up procedures |
| Caustic gouging / under-deposit corrosion | Water walls, high heat-flux zones | Irregular gouges under deposits | Concentrated caustic under porous deposits | Control boiler-water chemistry, chemical cleaning to remove deposits |
| Hydrogen damage | Water walls | Thick-edged “window” blow-out, no thinning | Acidic conditions under deposits (e.g. condenser leaks) release hydrogen into the steel | Stop condenser in-leakage, maintain pH, chemical cleaning |
| Oxygen pitting | Economisers, idle boilers | Round pits, often with oxide caps | Dissolved oxygen in feedwater or during lay-up | Deaeration, oxygen scavenging, correct wet/dry lay-up |
| Corrosion fatigue | Water walls at attachments, economiser inlets | Transverse cracks starting from the water side | Cyclic stress plus a corrosive water environment – frequent start/stop cycling | Reduce cycling stresses, improve attachment design, maintain water chemistry |
| Fly-ash / sootblower erosion | Economisers, low-temperature superheaters | Smooth, polished thinning on the gas side | High flue-gas velocity carrying ash; misaligned sootblowers | Flow baffles and shields, sootblower alignment, wear-resistant cladding |
| Fireside corrosion | Water walls (coal), superheaters | Wall thinning with external deposits | Sulphur, alkali and chlorine compounds in fuel ash, reducing atmospheres | Combustion tuning, weld overlay or coatings, higher-chromium alloys |
| Thermal fatigue | Superheater outlets, drains, attemperators | Circumferential cracks | Rapid temperature changes – quench from attemperator spray or condensate | Controlled ramp rates, proper drains, attemperator maintenance |
| Dissimilar metal weld failure | Ferritic–austenitic welds in superheaters | Crack along the fusion line | Thermal expansion mismatch and carbon migration at high temperature | Nickel-based filler metals, planned replacement intervals |
1. Overheating – the Most Common Cause
Long-term overheating (creep) happens when superheater or reheater tubes run a little above their design temperature for months or years. Internal steam-side oxide scale insulates the tube, the metal gets hotter, and the tube slowly swells until it ruptures with a thick, blunt edge. Short-term overheating is sudden – a blocked tube, low water level or loss of flow lets the metal reach very high temperatures within minutes, giving a thin-edged “fish-mouth” rupture.
Prevention: use the correct alloy for the metal temperature – carbon steel (A192, A210) for cooler sections and Cr-Mo grades such as T11, T22 and T91 for superheaters; monitor tube metal temperatures; remove steam-side scale; and keep start-up procedures and drum level under control.
2. Water-Side Corrosion – Water Wall Tube Failures
Most water wall tube failures start with internal deposits. Porous deposits let boiler-water chemicals concentrate against the tube wall, causing caustic gouging, or – where the water turns acidic, for example after a condenser leak – hydrogen damage, which makes the steel brittle and blows out a “window” without much thinning.
Prevention: keep boiler-water chemistry within limits, stop condenser in-leakage quickly, monitor deposit weight and chemically clean the boiler before deposits become heavy.
3. Oxygen Pitting
Boiler tube pitting is caused by dissolved oxygen – either in poorly deaerated feedwater or from air entering a boiler that is standing idle. Pits are small and deep and can perforate a tube long before the general wall has thinned. Economisers and boilers with frequent shutdowns are most at risk.
Prevention: efficient deaeration and oxygen control, and correct wet or dry lay-up whenever the boiler is out of service.
4. Corrosion Fatigue and Thermal Fatigue
Corrosion fatigue cracks start on the water side where the tube is restrained – at attachments, buckstays and economiser inlet headers – and grow with every start-up and shutdown. Thermal fatigue cracks come from rapid temperature swings, such as attemperator spray or condensate hitting hot tubes.
Prevention: limit cycling stresses with controlled ramp rates, improve attachment design, keep drains working and maintain water chemistry.
5. Erosion and Fireside Corrosion
On the gas side, fly-ash erosion thins tubes where flue-gas velocity is high, and badly aligned sootblowers cut tubes with steam jets. Fireside corrosion is caused by sulphur, alkali and chlorine compounds in the fuel ash, especially on coal-fired water walls and high-temperature superheaters.
Prevention: baffles and tube shields, sootblower maintenance, combustion tuning, weld overlay or coatings, and higher-chromium alloys where corrosion is severe.
Fire-Tube Boiler Corrosion
In fire-tube boilers the same rules apply on a smaller scale: oxygen pitting and scale on the water side, and acidic dew-point corrosion at the cold end of the tubes when flue gas condenses. Good feedwater treatment, blowdown and keeping flue-gas temperatures above the acid dew point prevent most problems. Fire-tube boilers commonly use ERW A178 or seamless A192 tubes.
What Causes Boiler Tube Leaks?
A boiler tube leak is the end result of one of the mechanisms above – thinning from erosion or corrosion, a pit, a fatigue crack or an overheating rupture. Poor welds and mechanical damage during maintenance also cause leaks. Finding the root cause matters: replacing the tube without fixing the cause usually means another leak nearby. Early detection methods include acoustic leak detection, rising make-up water demand, and UT thickness surveys during outages.
How to Prevent Boiler Tube Failures – Checklist
- Water chemistry: follow the boiler maker’s limits for pH, conductivity, oxygen and silica; act fast on condenser leaks.
- Deposits: measure deposit weight on sample tubes and chemically clean when needed.
- Temperatures: monitor tube metal and steam temperatures; avoid overfiring and flue-gas imbalance.
- Operation: controlled start-up and shutdown rates; correct lay-up during outages.
- Gas side: sootblower alignment, erosion shields, combustion tuning.
- Inspection: UT thickness, oxide-scale measurement, visual and NDT checks at every outage.
- Materials: use the right grade for each section and replace like-for-like or upgraded tubes – see the boiler tube material guide.
Choosing the Right Boiler Tube Material
| Boiler section | Common failure risks | Typical tube grades |
| Economiser | Oxygen pitting, fly-ash erosion, corrosion fatigue at inlet | A179, A192, A210 A-1 |
| Water walls | Caustic gouging, hydrogen damage, fireside corrosion, short-term overheating | A192, A210 C, T11 |
| Superheaters / reheaters | Long-term overheating (creep), steam-side oxidation, fireside corrosion | T11, T22, T91, T92 |
| Heat exchangers / condensers | Pitting, erosion | A179, A214 |
ASC LLP supplies replacement boiler tubes in all these grades – seamless, ERW and U-bent, with IBR certification available – for planned outages and emergency repairs. We supply ASTM A192 boiler tubes and A210 Grade C tubes in all sizes.
Boiler Tube Failures – FAQ
What is the most common cause of boiler tube failure?
Overheating is the most common cause: long-term overheating (creep) in superheater and reheater tubes, and short-term overheating when flow is lost or deposits block heat transfer. Water-side corrosion and fly-ash erosion are the next most common causes.
What causes boiler tube leaks?
Leaks are usually the end result of a damage mechanism – thinning from erosion or corrosion, pitting from dissolved oxygen, cracking from corrosion fatigue or thermal fatigue, or a bulge and rupture from overheating. Poor welds and mechanical damage during maintenance also cause leaks.
Why do water wall tubes fail?
Water wall tubes fail mainly from internal deposits combined with poor water chemistry, which leads to under-deposit corrosion such as caustic gouging and hydrogen damage, as well as fireside corrosion, short-term overheating and corrosion fatigue at attachments.
What causes pitting in boiler tubes?
Pitting is mostly caused by dissolved oxygen in feedwater or by oxygen entering during shutdowns. Good deaeration, oxygen scavengers or oxygenated treatment within limits, and proper wet or dry lay-up during outages prevent it.
How can boiler tube failures be prevented?
Control water chemistry and remove deposits, keep metal temperatures within design, manage sootblowing and flue-gas velocity to limit erosion, avoid rapid start-ups and shutdowns, inspect regularly with UT thickness and NDT, and use the correct tube grade for each section.
How is a boiler tube failure investigated?
Remove the failed section with an undamaged reference piece, record its location and operating history, then examine the fracture, wall thickness, deposits and microstructure. The appearance of the failure – thick-lipped, fish-mouth, pitted or cracked – points to the mechanism.
